DE102014204664A1 - Pressure sensor and method of manufacturing the pressure sensor - Google Patents

Abstract

The invention relates to a pressure sensor (100) having a substrate (102) and a transistor structure (104). The substrate (102) has a cavity (106) introduced into the substrate (102). The transistor structure (104) is arranged above the cavity (106). The transistor structure (104) has a flexible heterostructure (108) and at least one source contact (110) and drain contact (112) electrically connected to the heterostructure (108) and a gate contact (114). The heterostructure (108) is configured to assume a position corresponding to a pressure ratio between a first pressure in the cavity (106) and a second pressure on a side of the heterostructure (108) opposite the cavity. The transistor structure (104) is configured to provide an electrical signal corresponding to the position.

Description

State of the art

The present invention relates to a pressure sensor and to a method of manufacturing the pressure sensor.

A pressure sensor requires a pressure-sensitive membrane that separates two pressures. The membrane is deflected across the membrane according to a pressure difference. The deflection of the membrane is converted into an electrical signal.

The US 6 647 796 B2 describes a semiconductor nitride micro pressure sensor and a method for manufacturing the micro pressure sensor.

Disclosure of the invention

Against this background, with the approach presented here, a method for producing a pressure sensor, a pressure sensor, furthermore a device which uses the method and finally a corresponding computer program product according to the main claims are presented. Advantageous embodiments emerge from the respective subclaims and the following description.

In order to produce a chamber or a cavity, a placeholder can be arranged in a recess. The placeholder can serve as a structural element for supporting an occlusive layer in closing the recess. If the recess is closed, the placeholder can be removed and the cavity is created. In particular, a material of the placeholder in a first state displace more volume, as in a second state. To remove the placeholder, the material can be transferred from the first state to the second state. A volume shrinkage forms the volume of the chamber.

Advantageously, the recess can be closed by the placeholder with simple means cost. The resulting pressure sensor can have a high sensitivity, since a pressure-sensitive membrane of high quality can be produced by the approach presented here.

A method for manufacturing a pressure sensor is presented, the method comprising the following steps:
Providing a substrate for the pressure sensor;
Changing the substrate in a portion of the substrate provided for a cavity of the pressure sensor to obtain a modified substrate;
Depositing a heterostructure on a surface of the substrate in the region of the altered substrate;
Removing the altered substrate to create the cavity between the heterostructure and the substrate; and
Contacting the heterostructure with at least one each of a source contact, drain contact and gate contact to produce a transistor structure of the pressure sensor.

Furthermore, a pressure sensor with the following features is presented:
a substrate having a cavity introduced into the substrate; and a transistor structure disposed over the cavity, the transistor structure having a flexible heterostructure and at least one source contact and drain contact electrically connected to the heterostructure, and a gate contact, the heterostructure configured to have a position corresponding to a pressure ratio between a first one Pressure in the cavity and a second pressure on a side of the heterostructure opposite the cavity and the transistor structure is adapted to provide an electrical signal corresponding to the position.

A further embodiment provides for the 2-D electron gas without gate contact to be read purely resistively by means of source and drain contact.

A pressure sensor may be understood to mean a sensor for detecting a pressure in a medium. The pressure can be a static pressure or a dynamic pressure. To detect the pressure, a path of a membrane is detected. The path is dependent on a bending resistance moment of the membrane and a force on the membrane. The bending resistance torque is dependent on a thickness of the membrane and material characteristics of the membrane. The force on the membrane depends on a surface of the membrane and a pressure difference between a first pressure on a first side of the membrane and a second pressure on a second side of the membrane. If the pressure sensor is an absolute pressure sensor, then the pressure on one side of the diaphragm is a known pressure, which is compared to the pressure on the other side of the diaphragm. A pressure difference between the known pressure and the unknown pressure results in the force on the membrane. For this purpose, the pressure sensor adjacent to the membrane has a chamber or cavity in which the known pressure prevails. If the pressure sensor is a differential pressure sensor, then the pressures on both sides of the diaphragm are unknown, but the pressure differential between the two pressures results in force on the diaphragm. A substrate may be a starting material for the pressure sensor. The Substrate may be a semiconductor substrate. In particular, the substrate may be silicon. When changing, a structure of the substrate can be changed. The membrane may have at least one heterostructure. The heterostructure may be composed of at least two different layers of material. Source contact, drain contact, and gate contact may be electrically conductive terminals that are in direct or indirect contact with the heterostructure. Source contact, drain contact, and gate contact form the heterostructure into a transistor structure.

The method may include a step of growing a carrier layer for the heterostructure on the altered substrate. A carrier layer may consist of a semiconductor material. The carrier layer may be made of the same material as the substrate. Carrier layer can become part of the substrate. By the carrier layer, the bending stiffness of the membrane can be influenced. A thicker membrane can withstand greater forces. A thinner membrane can have a higher sensitivity. The carrier layer can improve a tightness of the cavity.

The method may include a step of introducing an electrical circuit into the substrate, wherein the electrical circuit is electrically connected to the transistor structure. The circuit may be a microelectronic circuit. The circuit can be produced using manufacturing steps of semiconductor technology. The circuit may be arranged at a small distance from the transistor structure. Due to the small distance, the circuit can utilize pressure signals with a very low amplitude.

The method may include a step of opening the cavity whereby the substrate is broken to provide a differential pressure sensor. The substrate may be broken on a side opposite the membrane. Then, the pressure sensor may be disposed between a first volume and a second volume to detect a differential pressure between a first pressure in the first volume and a second pressure in the second volume.

In the contacting step, an insulating layer may be disposed between the heterostructure and the gate contact. An insulating layer can influence an electrical conductivity of the heterostructure using an electric field of the gate electrode.

The insulating layer prevents current flow between the heterostructure and the gate electrode.

In the step of changing the modified substrate can be changed by anodizing, wherein the substrate is particularly porous by the anodization. In anodizing, the substrate can be altered using electrical energy. A porous substrate may have a lower density than the substrate.

In the depositing step, at least two semiconductor materials with different band gaps can be deposited on each other to produce the heterostructure. Due to the different size band gaps, an electron gas can arise between the semiconductor materials. In the electron gas, electrons can be moved toward a plane of the layers with little resistance. Transverse to the plane of the layers, the electrons can be moved with a large resistance. Due to the electron gas, a pressure sensor with a particularly high sensitivity can be produced. The semiconductor heterostructure may consist of a sequence of two compound semiconductors of the elements of the III-V groups. The heterostructure can be formed, for example, by the sequence GaN / AlGaN.

Also advantageous is an embodiment of the approach presented here, with a step of thinning the heterostructure to a predetermined thickness, in particular wherein the thinning is carried out using a chemical-mechanical polishing. It can be achieved by subsequent merger under reference conditions, eg. B. a specified pressure, with a pre-structured substrate, a cavity with a carrier layer and an absolute pressure sensor arise. Such an embodiment of the approach presented here offers the advantage of a particularly simple and cost-effective production possibility.

In the removal step, the modified substrate can be dissolved by a heat treatment. By a heat treatment, the modified substrate can melt. During melting, the material of the modified substrate can occupy as small a surface as possible. In this case, a volume of the modified substrate can shrink. By shrinking the cavity can arise. In the cavity, a vacuum can be created approximately.

The approach presented here also creates a device that is designed to implement or implement the steps of a variant of a method presented here in corresponding devices. Also by this embodiment of the invention in the form of a device, the object underlying the invention can be solved quickly and efficiently.

In the present case, a device can be understood as meaning an electrical device which processes sensor signals and outputs control and / or data signals in dependence thereon. The device may have an interface, which may be formed in hardware and / or software. In the case of a hardware-based embodiment, the interfaces can be part of a so-called system ASIC, for example, which contains a wide variety of functions of the device. However, it is also possible that the interfaces are their own integrated circuits or at least partially consist of discrete components. In a software training, the interfaces may be software modules that are present, for example, on a microcontroller in addition to other software modules.

Also of advantage is a computer program product or computer program with program code which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and for carrying out, implementing and / or controlling the steps of the method according to one of the embodiments described above is used, especially when the program product or program is executed on a computer or a device.

The approach presented here will be explained in more detail below with reference to the accompanying drawings. Show it:

1 an illustration of a pressure sensor according to an embodiment of the present invention;

2 a representation of a pressure sensor with a carrier layer according to an embodiment of the present invention;

3 a representation of a pressure sensor with an insulating layer according to an embodiment of the present invention; and

4 a flowchart of a method for manufacturing a pressure sensor according to an embodiment of the present invention.

In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and similar acting, with a repeated description of these elements is omitted.

1 shows a representation of a pressure sensor 100 according to an embodiment of the present invention. The pressure sensor 100 has a substrate 102 and a transistor structure 104 on. In the substrate 102 is a cavity 106 brought in. Above the cavity 106 is the transistor structure 104 arranged. The transistor structure 104 closes the cavity 106 , The transistor structure 104 has a flexible heterostructure 108 and at least one source contact 110 or a source electrode 110 , at least a drain contact 112 or a drain electrode 112 and at least one gate contact 114 or a gate electrode 114 on. The heterostructure 108 is one, the cavity 106 formed fluid-tight closing, flexible membrane. The source contact 110 is electrically conductive with a first side of the heterostructure 108 connected. The drain contact 112 is electrically conductive with a second side of the heterostructure opposite the first side 108 connected. The gate contact 114 is on a side of the heterostructure opposite the cavity 108 arranged. The heterostructure 108 is adapted to a position corresponding to a pressure ratio between a first pressure in the cavity 106 and a second pressure on the opposite side of the heterostructure 108 take. The transistor structure 104 is configured to provide an electrical signal corresponding to the position.

The cavity 106 is during the manufacture of the pressure sensor 100 by converting material of the substrate 102 into an altered substrate and then removing the altered substrate. Before removing the altered substrate is the heterostructure 108 on the surface of the substrate 102 and the modified substrate. After an at least partial construction of the heterostructure 108 the modified substrate has been removed.

In one embodiment, the material of the substrate 102 made of silicon and was changed by anodizing, so that the material has become porous. The porous material is less heat resistant than the original material of the substrate 102 , During a heat treatment in which the heterostructure 108 is built up, the porous material has dissolved and contracted to form the smallest possible surface. The cavity 106 has remained as a cavity. Because the heterostructure 108 as well as the substrate 102 are fluid tight, is within the cavity 106 formed approximately a vacuum.

The pressure sensor 100 is configured to provide an electrical signal representing a difference between the pressure within the cavity 106 and a pressure on the opposite side of the heterostructure 108 represents. Due to the pressure difference on both sides of the Heterostructure acts as a resultant force on the heterostructure 108 , The force bends the heterostructure 108 or the membrane. The bending changes an electrical conductivity of the heterostructure 108 , The electrical signal represents the changed electrical conductivity.

In one embodiment, the pressure sensor 100 an electrical circuit. The circuit is in the substrate during fabrication 102 been introduced. The circuit may be mounted on the front or back of the substrate by appropriate methods of semiconductor technology. The electrical circuit is with the transistor structure 104 electrically connected. The circuit is adapted to the electrical signal of the transistor structure 104 to process or to reinforce.

In one embodiment, the pressure sensor 100 an open cavity. The substrate 102 is broken across the membrane. Through the opening to the cavity is the pressure sensor 100 designed as a differential pressure sensor.

In a specific embodiment shows 1 a GaN-HEMT pressure sensor 100 according to the approach presented here. The pressure sensor 100 has a pressure-sensitive part of a III / V heterostructure 108 without supporting substrate. The heterostructure 108 is part of a transistor 104 ,

2 shows a representation of a pressure sensor 100 with a carrier layer 200 according to an embodiment of the present invention. The pressure sensor 100 essentially corresponds to the pressure sensor in 1 , In addition, the pressure sensor points 100 the carrier layer 200 between the heterostructure 108 and the cavity 106 on. The carrier layer 200 is fixed with the heterostructure 108 connected. The carrier layer 200 is thus an integral part of the cavity 106 occlusive membrane. The carrier layer 200 is when making the pressure sensor 100 on the surface of the substrate 102 and the altered substrate grown. The carrier layer 200 is thus also part of the substrate 102 , The carrier layer 200 includes the modified substrate. During the further manufacturing process, the modified substrate dissolves and forms the cavity 106 out. The carrier layer promotes the deposition of the heterostructure 108 and consists for example of epitaxially grown silicon. A thickness of the carrier layer 200 significantly determines the flexural strength of the heterostructure 108 , The thicker the membrane from the carrier layer 200 and the heterostructure 108 is, the more she is. The more rigid the membrane, the lower is a deflection of the membrane at the same pressure difference. In other words, a sensitivity of the pressure sensor 100 larger, the thinner the membrane is.

Another embodiment provides that the heterostructure 108 in a separate process on a carrier layer 200 or substrate is grown, which z. B. by CMP (chemical-mechanical polishing) is brought to a required thickness. By merging z. B. in the direct-bond process of an already prestructured substrate 102 creates a cavity 106 with a carrier layer 200 corresponding 2 , This design offers a great advantage for the manufacturability in large quantities.

In the deposition step, two semiconductor layers of different size bandgaps may be deposited on each other to create the heterostructure.

In this embodiment, the heterostructure is 108 from two layers 202 . 204 constructed of different semiconductor material. The at least two semiconductor materials have different sized band gaps. Between the layers 202 . 204 a two-dimensional electron gas is formed in an extending direction of the layers 202 . 204 has a high electrical conductivity. To the growth process of the layers 202 and 204 To favor, an additional transition or buffer layer can be used. By choosing a suitable transition layer, the layers 202 and 204 heteroepitaktisch on the carrier layer 200 to be grown.

The layers 202 . 204 are large on the surface of the substrate 102 or the carrier layer 200 been separated. The source contact 110 and the drain contact 112 are electrically connected by deposition and use of a thermal process with the electron gas along the heterostructure.

The HEMT transistor 104 (High-Electron Mobility Transistor, transistor with high electron mobility) is a special design of the field effect transistor, which is characterized by a conductive channel with a high charge carrier mobility. The structure of the HEMT transistor 104 consists of layers 202 . 204 different semiconductor materials with different sized band gaps, which has a heterostructure 108 form. For this purpose, in particular compound semiconductors come into question, which consist of elements of the III / V group of the periodic table. For example, the material system GaN / AlGaN can be used. If these two materials are separated, a two-dimensional electron gas (2DEG) is formed at the interface of these materials on both sides of the GaN, which serves as a conductive channel since the electron mobility is typically very high, typically 2000 cm ² / Vs. The reason for the formation of the electron gas is a superposition of the spontaneous polarizations in the GaN and AIGaN layers 202 . 204 with the piezoelectric polarization in the AIGaN layer caused by stress. Thanks to the high electrical electron mobility, this material system is particularly suitable for power electronic applications, moreover, the property of the electron gas also allows the production of a highly sensitive pressure sensor 100 ,

To an absolute pressure sensor 100 For example, to realize on GaN / AIGaN basis, he has a defined cavity 106 with reference pressure and a corresponding membrane 108 on.

By the approach presented here can in the production of the membrane 108 to dispense with a wet-chemical or dry-chemical etching process. Furthermore, there is the advantage of being able to dispense with a complicated sequence of differently doped GaN layers. The approach presented here makes it possible to obtain less expensive and more technologically mature, simple GaN / AIGaN heterostructures 108 to use.

It becomes an absolute pressure sensor 100 presented on a III / V heterostructure 108 based. The preparation is based on a process for producing a membrane 108 using porous silicon that demonstrates the use of the standard setup of GaN / AIGaN heterostructures 108 from the microwave technology or power electronics allowed.

In other words shows 2 a cross section of a pressure sensor 100 according to an embodiment of the present invention, based on a III / V heterostructure 108 , The heterostructure 108 is through two ohmic contacts 110 . 112 and a HEMT gate 114 to a transistor structure 104 educated. The first shift 202 the heterostructure 108 consists of GaN or gallium nitride. The second layer 204 the heterostructure 108 consists of AIGaN or aluminum gallium nitride. The substrate 102 consists of silicon ( 111 ).

3 shows a representation of a pressure sensor 100 with an insulating layer 300 according to an embodiment of the present invention. The pressure sensor 100 essentially corresponds to the pressure sensor in 2 , In addition, there is between the heterostructure 108 and the gate electrode 114 or the gate contact 114 the insulating layer 300 arranged. The insulating layer 300 isolates the gate electrode 114 electrically from the heterostructure 108 ,

In other words shows 3 a cross section of a pressure sensor 100 according to an embodiment of the present invention, based on a III / V heterostructure 108 , The heterostructure 108 is through two ohm contacts 110 . 112 and a MISFET gate 114 with insulator 300 to a transistor structure 104 educated. The first shift 202 the heterostructure 108 consists of GaN or gallium nitride. The second layer 204 the heterostructure 108 consists of AIGaN or aluminum gallium nitride. The substrate 102 consists of silicon ( 111 ).

4 shows a flowchart of a method 400 for manufacturing a pressure sensor according to an embodiment of the present invention. The procedure 400 has a step 402 of providing a step 404 of changing, one step 406 of depositing, one step 408 removing and one step 410 of contacting. In step 402 the provision of a substrate for the pressure sensor is provided. In step 404 of varying the substrate is changed in a, provided for a cavity of the pressure sensor portion of the substrate to obtain a modified substrate. In step 406 During deposition, a heterostructure is deposited on a surface of the substrate in the region of the altered substrate. In step 408 the removal removes the altered substrate to create the cavity between the heterostructure and the substrate. In step 410 contacting, the heterostructure is provided with at least one source contact, drain contact, and gate contact to produce a transistor structure of the pressure sensor.

Before the step 406 the deposition may be a step of growing up. In this case, a carrier layer for the heterostructure is grown on the modified substrate and / or the surface of the substrate.

A cavity below a GaN / AIGaN heterostructure can be obtained by the method described here 400 will be realized. For this purpose, a <111> substrate is used. Therein, porous silicon is generated by anodizing in the areas where the cavity (s) are to be formed.

Then an HEMT structure is produced by MOCVD growth. For this purpose, a low-temperature AIN-seed layer or aluminum nitride seed layer with, for example, about ten nanometers to 1000 nm at 400 ° C to 800 ° C is applied. This is followed by an in situ anneal or annealing at greater than 1000 ° C, at which the porous Si dissolves. The cavity is created where previously porous silicon was generated. At the seed layer, a GaN / AIGaN heterostructure is observed at the grown at conventional MOCVD temperatures of 1000 ° C to 1200 ° C.

The HEMT device fabrication is then performed by an interdevice isolation, for example by implantation or mesa etching. A gate connection is made by a Schottky contact or an MIS contact. Ohmic contacts, metallizations and passivations complete the HEMT structure.

Alternatively, before the MOCVD epitaxy, a thin, in particular smaller one micron to a few μm, Si epitaxy can be carried out.

From the back, a trench can be created so that the sensor can be used as a differential pressure sensor. In this case, the substrate can be thinned to simplify this process step.

In a further embodiment, electronic circuits are realized directly in the vicinity of the pressure sensor, thus, for example, additional functions such as signal processing or signal amplification can be monolithically integrated.

A pressure range of the pressure sensor presented here can be adjusted by a suitable choice of the grown GaN / AlGaN layer or Si epitaxial layer. Due to the very good electrical properties of GaN / AIGaN HEMTs, the pressure sensor has a high sensitivity.

By using the porous silicon as a placeholder for the cavity results in a simple process management.

A pressure sensor produced in this way has a high resistance to harsh environmental conditions. Due to the high chemical inertness of the GaN / AIGaN layers, the sensor can also be operated in harsh environmental conditions, such as high temperatures or corrosive atmospheres. This is particularly advantageous for automotive applications.

A quality of the manufacturing process can be checked by known methods such as SEM, FIB, TEM, XPS. The active heterostructure layer and the cavity can be recognized so well.

The sensor according to the approach presented here can be used for example as an absolute pressure sensor and / or as a differential pressure sensor in the field of consumer electronics and automotive electronics. In particular, the sensor can be used in applications requiring high sensitivity with high robustness, such as combustion chamber pressure sensors.

The embodiments described and shown in the figures are chosen only by way of example. Different embodiments may be combined together or in relation to individual features. Also, an embodiment can be supplemented by features of another embodiment.

Furthermore, the method steps presented here can be repeated as well as executed in a sequence other than that described.

If an exemplary embodiment comprises a "and / or" link between a first feature and a second feature, then this is to be read so that the embodiment according to one embodiment, both the first feature and the second feature and according to another embodiment either only first feature or only the second feature.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6647796 B2 [0003]

Claims (13)

Procedure ( 400 ) for producing a pressure sensor ( 100 ), the process ( 400 ) includes the following steps: providing ( 402 ) of a substrate ( 102 ) for the pressure sensor ( 100 ); Change ( 404 ) of the substrate ( 102 ) in one, for a cavity ( 106 ) of the pressure sensor ( 100 ) provided subregion of the substrate ( 102 ) to a modified substrate ( 102 ) to obtain; Separating ( 406 ) of a heterostructure ( 108 ) on a surface of the substrate ( 102 ) in the region of the modified substrate ( 102 ); Remove ( 408 ) of the modified substrate ( 102 ) to the cavity ( 106 ) between the heterostructure ( 108 ) and the substrate ( 102 ) to create; and contacting ( 410 ) of the heterostructure ( 108 ) with at least one source contact ( 110 ), Drain contact ( 112 ) and gate contact ( 114 ) to a transistor structure ( 104 ) of the pressure sensor ( 100 ) to create. Procedure ( 400 ) according to claim 1, comprising a step of growing a carrier layer for the heterostructure ( 108 ) on the modified substrate ( 102 ). Procedure ( 400 ) according to one of the preceding claims, with a step of introducing an electrical circuit into the substrate ( 102 ), wherein the electrical circuit with the transistor structure ( 104 ) is electrically connected. Procedure ( 400 ) according to one of the preceding claims, with a step of opening the cavity ( 106 ), the substrate ( 102 ) is broken to a differential pressure sensor ( 100 ) to accomplish. Procedure ( 400 ) according to one of the preceding claims, wherein in step ( 410 ) of contacting an insulation layer ( 300 ) between the heterostructure ( 108 ) and the gate contact ( 114 ) is arranged. Procedure ( 400 ) according to one of the preceding claims, wherein in step ( 404 ) of changing the modified substrate ( 102 ) is changed by anodizing, wherein the substrate ( 102 ) becomes particularly porous by the anodization. Procedure ( 400 ) according to one of the preceding claims, wherein in step ( 406 ) of depositing at least two semiconductor materials ( 202 . 204 ) are deposited on each other with band gaps of different size in order to reduce the heterostructure ( 108 ) to create. Procedure ( 400 ) according to any one of the preceding claims, comprising a step of thinning the heterostructure ( 108 ) to a predetermined thickness, in particular wherein the thinning is performed using chemical mechanical polishing. Procedure ( 400 ) according to one of the preceding claims, wherein in step ( 408 ) removing the modified substrate ( 102 ) is dissolved by a heat treatment. Pressure sensor ( 100 ) having the following characteristics: a substrate ( 102 ) with a into the substrate ( 102 ) introduced cavity ( 106 ); and a transistor structure ( 104 ) above the cavity ( 106 ), wherein the transistor structure ( 104 ) a flexible heterostructure ( 108 ) and at least one electrically conductive with the heterostructure ( 108 ) source contact ( 110 ) and drain contact ( 112 ) and a gate contact ( 114 ), wherein the heterostructure ( 108 ) is adapted to a position corresponding to a pressure ratio between a first pressure in the cavity ( 106 ) and a second pressure on a side of the heterostructure ( 108 ) and the transistor structure ( 104 ) is adapted to provide an electrical signal corresponding to the position. Device that is designed to perform and / or implement all steps of a method according to one of claims 1 to 9. Computer program that is set up to control and / or implement all steps of a method according to one of claims 1 to 9. A machine-readable storage medium having a computer program stored thereon according to claim 12.

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